I have a simple script to check whether webpage contains a specified string. It looks like:
#!/bin/bash
res=`curl -s "http://www.google.com" | grep "foo bar foo bar" | wc -l`
if [[ $res == "0" ]]; then
echo "OK"
else
echo "Wrong"
fi
As you can see, I am looking to get "OK", but got a "Wrong".
What's wrong with it?
If I use if [ $res == "0" ], it works. If I just use res="0" instead of res=curl..., it also can obtain the desired results.
Why are there these differences?
You could see what res contains: echo "Wrong: res=>$res<"
If you want to see if some text contains some other text, you don't have to look at the length of grep output: you should look at grep's return code:
string="foo bar foo bar"
if curl -s "http://www.google.com" | grep -q "$string"; then
echo "'$string' found"
else
echo "'$string' not found"
fi
Or even without grep:
text=$(curl -s "$url")
string="foo bar foo bar"
if [[ $text == *"$string"* ]]; then
echo "'$string' found"
else
echo "'$string' not found in text:"
echo "$text"
fi
od -c <<< "$res"? Are there extra whitespace characters?I found the answer in glenn jackman's help.
I get the following points in this question:
wc -l 's output contains whitespaces.echo "$var" instead of echo $var[[ preserves the literal value of all characters within the var.[ expands var to their values before perform, it's because [ is actually the test cmd, so it follows Shell Expansions rules.